[llvm] [LLVM][rtsan] Add LLVM nosanitize_realtime attribute (PR #105447)

[Chris Apple via llvm-commits]

cjappl wrote:

> So do you really need the LLVM attributes then? Would it not suffice to have Clang IRGen add the calls to `__rtsan_bypass_on/off` and `__rtsan_realtime_enter/exit` based on the Clang attributes? The other sanitizers have passes because they need to be able to operate on arbitrary instructions in each function after optimization, but if RTSan only needs to affect function entry/exit then that seems much more straightforwardly accomplished in the frontend.

We discussed this a bit in the RFC thread (apologies in advance for the size of it, it became a monster), this comment and below:
https://discourse.llvm.org/t/rfc-nolock-and-noalloc-attributes/76837/104?u=cjappl

The reasoning we came up with to have it be in LLVM directly is in this comment:
https://discourse.llvm.org/t/rfc-nolock-and-noalloc-attributes/76837/107?u=cjappl


https://github.com/llvm/llvm-project/pull/105447